As described more fully in now commonly-owned copending U.S. application Ser. No. Case OR-7006!, filed Nov. 22, 1996, tetrakis(dihydrocarbylamino)phosphonium halides are useful as catalysts in halogen exchange reactions between alkali metal fluorides, such as KF, and chloro- and bromoaromatics, such as hexachlorobenzene. A variety of useful fluorinated aromatic compounds can be produced in this manner.
A laboratory synthesis method for the preparation of tetrakis(dihydrocarbylamino)phosphonium halides, is described by Koidan, Marchenko, Kudryavtsev, and Pinchuk, Zh. Obshch. Khim., 1982, 52, 2001, an English language translation of which is available from Plenum Publishing Corporation.
Another prior process to form a tetrakis(dialkylamino)phosphonium halide involves the reaction of tris(dialkylamino)phosphoroamidite with one equivalent of an alkyl halide. The reported yield of the tetrakis(dialkylamino)phosphonium halide was 38.5%. In addition, this prior process involved forming the tetrakis(dialkylamino)phosphonium halide in two stages in separate reactors. The first stage involved reacting a tris(dialkylamino)phosphoroamidite hydrochloride with a small excess of sodium hydroxide to free the phosphoroamidite of the hydrogen chloride. After working up this reaction mixture, the HCl-free tris(dialkylamino)phosphoroamidite was isolated and then subjected in the second reactor to the foregoing reaction with one equivalent of the alkyl halide.
A need exists for a process enabling more efficient production of tetrakis(dihydrocarbylamino)phosphonium halides, especially if the process is capable of being effectively used in large scale production facilities while satisfying the economic constraints of commercial operations. This invention is deemed to satisfy these objectives.